Fine tuning of emission spectra by combination of multiple emitter spectra

ABSTRACT

A first device is provided. The first device includes an anode, a cathode and an emissive layer disposed between the anode and the cathode. The emissive layer includes a first organic emitting material having a first peak wavelength and a second organic emitting material having a second peak wavelength. The emissive layer has a homogenous composition. The second peak wavelength is between 0 and 40 nm greater than the first peak wavelength.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices havingdesired emission characteristics, and methods of fabricating suchdevices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

As used herein, and as would be generally understood by one of skill inthe art, the term “emitting” as used to describe a material in a devicerefers to a material that emits a significant amount of light when thedevice is operated under normal conditions. For example, Ir(ppy)₃ is awell known emissive organic material. Ir(ppy)₃ may be used as anemitting material in an OLED, generally by including it in the emissivelayer with a host, in a device designed such that recombination occursin or near the layer containing Ir(ppy)₃, and such that emission fromthe Ir(ppy)₃ is energetically favored. However, Ir(ppy)₃ may also beused in an OLED as a material that is not an “emitting” material. Forexample, it is known to use Ir(ppy)₃ as a hole transport material in ahole transport layer, such that the Ir(ppy)₃ functions to transportholes to an emissive layer where a different material emits light. Inthis context, Ir(ppy)₃ is not considered an “emitting” material.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

A first device is provided. The first device includes an anode, acathode and an emissive layer disposed between the anode and thecathode. The emissive layer includes a first organic emitting materialhaving a first peak wavelength and a second organic emitting materialhaving a second peak wavelength. The emissive layer has a homogenouscomposition. The second peak wavelength is between 0 and 40 nm greaterthan the first peak wavelength.

In one embodiment, the first and second organic emitting materials arephosphorescent organic light emitting materials.

Preferably, the second peak wavelength is between 12 and 28 nm greaterthan the first peak wavelength.

In some embodiments, first device of claim 1, the first device emits athird peak wavelength that is between the first peak wavelength and thesecond peak wavelength. Preferably, the concentration of the firstorganic emitting material in the emissive layer is C1, the concentrationof the second organic emitting material in the emissive layer is C2, thefirst, second and third peak wavelengths are λ1, λ2, and λ3,respectively, and the third peak wavelength λ3 is within 4% of:((λ1C1)+(λ2C2))/(C1+C2).

In some embodiments, wherein the FWHM of the emissive spectrum of thefirst device is less than the greater of the FWHM of the emissivespectrum of (i) a second device that is the same as the first device inall respects except that it includes the first emitting material but notthe second emitting material, and (ii) a third device that is the sameas the first device in all respects except that it includes the secondemitting material but not the first emitting material.

In some embodiments, the measured FWHM of the emissive spectrum of thefirst device is less than the combined emission of the first and secondemitting materials calculated based on the proportions of the first andsecond emitting materials present in the emissive layer. In someembodiments, the measured FWHM of the emissive spectrum of the firstdevice is at least 10% less than the combined emission of the first andsecond emitting materials calculated based on the proportions of thefirst and second emitting materials present in the emissive layer.

In some embodiments, the first device is an organic light emittingdevice.

In some embodiments, the first device is a panel that includes aplurality of organic light emitting devices controlled by an activematrix.

In some embodiments, the first device is a consumer product.

A method of fabricating a first device is provided. A first container isprovided that contains, in a desired proportion: a first organicemitting material having a first peak wavelength, and a second organicemitting material having a second peak wavelength. A substrate isprovided having a first electrode disposed thereon. An emissive layer isdeposited over the first electrode, wherein the first container is asource of material for depositing, and wherein the emissive layercomprises the first and second organic emitting materials in the desiredproportion. A second electrode over the first emissive layer. The secondpeak wavelength is between 0 and 40 nm greater than the first peakwavelength.

In some embodiments, depositing the emissive layer further comprisesdepositing an organic host along with the first and second organicemitting materials. The organic host may be included in and depositedfrom the first container, and/or may be deposited from a secondcontainer.

Embodiments and preferences discussed above with respect to devices arealso applicable to methods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a schematic structure of devices that were fabricatedhaving variable [%] of emitters C and D, used with Example 1.

FIG. 4 shows electroluminescent (EL) spectra of the devices of Example1.

FIG. 5 shows maximum wavelength and full width half maximum (FWHM)values for the devices of Example 1. Both measured experimental data andresults calculated by adding spectra proportional to emitterconcentration are shown.

FIG. 6 shows the FWHM difference (experimental vs. calculated) valuesfor the devices of Example 1.

FIG. 7 shows schematic structure for the devices of Example 2 withvariable [%] of emitters A and B.

FIG. 8 shows EL spectra of the devices of Example 2 with variable [%] ofemitters A and B.

FIG. 9 shows maximum wavelength and FWHM values for the devices inExample 2 with variable [%] of emitters A and B. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

FIG. 10 shows a schematic structure for the devices in Example 3 withvariable [%] of emitters B and C.

FIG. 11 shows EL spectra for the devices of Example 3 with variable [%]of emitters B and C.

FIG. 12 shows maximum wavelength and FWHM values for the devices ofExample 3 with variable [%] of emitters B and C. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

FIG. 13 shows a schematic structure for the devices of Example 4 withvariable [%] of emitters A and D.

FIG. 14 shows EL spectra for the devices of Example 4 with variable [%]of emitters A and D.

FIG. 15 shows maximum wavelength and FWHM values for the devices ofExample 4 with variable [%] of emitters A and D. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

FIG. 16 shows a schematic structure for the devices of Example 5 withvariable [%] of emitters B and D.

FIG. 17 shows EL spectra for the devices of Example 5 with variable [%]of emitters B and D.

FIG. 18 shows maximum wavelength and FWHM values for the devices ofExample 5 with variable [%] of emitters B and D. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

FIG. 19 shows chemical structures for compounds used in devicefabrication.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” LED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

A first device is provided. The first device includes an anode, acathode and an emissive layer disposed between the anode and thecathode. The emissive layer includes a first organic emitting materialhaving a first peak wavelength and a second organic emitting materialhaving a second peak wavelength. The emissive layer has a homogenouscomposition. The second peak wavelength is between 0 and 40 nm greaterthan the first peak wavelength.

The first device may include other emissive layers that do notnecessarily meet the criteria described in the preceding paragraph. Forexample, the first device may include a first emissive layer that doesmeet the criteria of the preceding paragraph, such as inclusion of thefirst and second organic emitting materials as specified. The firstdevice may further include a second organic emissive layer that does notmeet the criteria, and that may, for example, have only a singleemitting material, or a non-homogenous composition.

It is known to fabricate an OLED having multiple emitting materials,both in the same layer and in different layers. However, these OLEDs aregenerally directed to achieving broad spectrum emission. Thus, it isknown, for example, to combine green and red emitting materials in asingle layer. In this situation, triplets tend to transfer from thehigher energy green emitters to the lower energy red emitters, such thatproportion of emission from the lower energy red emitters relative tothe green emitters may be significantly larger than the proportion ofthe concentration of red emitter to green emitter. To achieve balancedemission in this situation, those of skill in the art expect that theconcentration of red emitter be much lower than the concentration ofgreen emitter. The combined red-green emission may be further combinedwith blue emission from another layer in the same device, or blueemission from a different device, to achieve broad spectrum emission.

The purpose of embodiments disclosed herein is significant different.Embodiments disclosed herein are directed to using two differentemitters in the same layer that emit similar spectra having similar peakwavelengths, with the goal of fine tuning the emission to a specificdesired spectra. The desired spectra may be, for example, particularspectra of red, green and blue to which the human eye is particularlysensitive, and which may be required by certain manufacturing standards.By using fine tuning as disclosed herein, it is possible to use to emita specific desired color two particularly good emitters in terms oflifetime, stability, efficiency, cost, ease of fabrication and the like.While each of the two particularly good emitters may not on their ownemit the specific desired color, their emission may be combined asdescribed herein to achieve the specific desired color.

In one embodiment, the first and second organic emitting materials arephosphorescent organic light emitting materials.

Preferably, the second peak wavelength is between 12 and 28 nm greaterthan the first peak wavelength.

The inventors have found, when combining two emitting materials in thesame layer that have somewhat similar peak wavelengths as describedhere, that the peak wavelength is unexpectedly theconcentration-weighted average peak wavelength of the two individualemitting material. This is contrary to conventional wisdom, whichpredicts that triplets will preferentially transfer to the lower energymaterial, such that the proportion of emission from the lower energyemitting material compared to the higher energy emitting material isexpected to be more than the proportion of its concentration. Thus, insome embodiments, first device of claim 1, the first device emits athird peak wavelength that is between the first peak wavelength and thesecond peak wavelength. Preferably, the concentration of the firstorganic emitting material in the emissive layer is C1, the concentrationof the second organic emitting material in the emissive layer is C2, thefirst, second and third peak wavelengths are λ1, λ2, and λ3,respectively, and the third peak wavelength λ3 is within 4% of:((λ1C1)+(λ2C2))/(C1+C2).

In some embodiments, wherein the FWHM of the emissive spectrum of thefirst device is less than the greater of the FWHM of the emissivespectrum of: (i) a second device that is the same as the first device inall respects except that it includes the first emitting material but notthe second emitting material, and (ii) a third device that is the sameas the first device in all respects except that it includes the secondemitting material but not the first emitting material.

“FWHM” or full width half maximum is a term known to the art that refersto the width of a peak at one half of the peak's maximum intensity. Inthe context of emissive spectra, FWHM is a measure of whether a spectrumis narrow or broad. Generally, narrow peaks have a smaller FWHM thanbroader peaks. A small FWHM corresponds to a narrow peak, which may alsobe referred to as more “saturated” than a broader peak. Saturatedspectra are desirable in certain contexts, such as for use in displaysthat do not use color filters. Broad spectrum peaks are useful in othercontexts, such as for use in displays that do use color filters, or toemit light for general illumination purposes with a high “CRI” (colorrendering index).

The inventors have discovered that, when two emitters are combined inthe same emissive layer as described herein, that the width of the totalspectra is often less than expected from a calculation based on summingthe contributions of the individual emitters. This result is observed inExamples 1, 3, 4 and 5. This result is unexpected. The “width” of aspectrum may be quantified using FWHM. Indeed, the inventors haveobserved many situations where the width of the total spectrum is evennarrower, less than the width of one or preferably both of the spectraof the individual emitting materials that contribute to the totalspectrum. This result is also unexpected. While not intending to belimited to any theory of why embodiments of the invention work, theinventors believe that the narrower than expected spectra are the resultof the solvachromatic effect, as discussed, for example, in WO99-053724Color-tunable organic light emitting devices. Forrest, Stephen R.;Bulovic, Vladimir; Thompson, Mark E.; Shoustikov, Andrei.

In some embodiments, the measured FWHM of the emissive spectrum of thefirst device is less than the combined emission of the first and secondemitting materials calculated based on the proportions of the first andsecond emitting materials present in the emissive layer. In someembodiments, the measured FWHM of the emissive spectrum of the firstdevice is at least 4% less than the combined emission of the first andsecond emitting materials calculated based on the proportions of thefirst and second emitting materials present in the emissive layer.

In some embodiments, the first device is an organic light emittingdevice.

In some embodiments, the first device is a panel that includes aplurality of organic light emitting devices controlled by an activematrix.

In some embodiments, the first device is a consumer product.

A method of fabricating a first device is provided. A first container isprovided that contains, in a desired proportion: a first organicemitting material having a first peak wavelength, and a second organicemitting material having a second peak wavelength. A substrate isprovided having a first electrode disposed thereon. An emissive layer isdeposited over the first electrode, wherein the first container is asource of material for depositing, and wherein the emissive layercomprises the first and second organic emitting materials in the desiredproportion. A second electrode over the first emissive layer. The secondpeak wavelength is between 0 and 40 nm greater than the first peakwavelength.

In some embodiments, depositing the emissive layer further comprisesdepositing an organic host along with the first and second organicemitting materials. The organic host may be included in and depositedfrom the first container, and/or may be deposited from a secondcontainer.

Embodiments and preferences discussed above with respect to devices arealso applicable to methods described herein.

The principle of fine emission tuning of the EL device spectrum isdisclosed. As described herein, desirable emission spectrum can beobtained by combination of individual emitters spectra with certainratio. If 2 emitters with λ1 and λ2 maximum wavelengths where λ1<λ2 aremixed in the device EML in certain ratio, then the maximum wavelength ofthe resulting device λ3 can be fine tuned within range from λ1 to λ2 bythe tuning the relative concentrations of the emitters in the device EMLand proportional to the emitters concentration.

The maximum wavelength λ3 of EL or PL emission of the device may betuned to values between λ1 to λ2 max individual emitter wavelengths bythe combination of individual emitters emission in the device, which canbe achieved by placing of 2 corresponding emitters into the device EMLin a desired concentration ratio. It has been shown that the maximumcombined wavelength λ3 will be within λ1 and λ2 range and directlyproportional to emitters concentration.

The combination of 2 emitter emission described herein may be useful forfine tuning device emission for a specific wavelength, e.g. to match aspecific spectrum requirement for various applications. Suchapplications include OLED based flat panel displays and lighting.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but not limit to: aphthalocyanine or porphryin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and sliane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

k is an integer from 1 to 20; X¹ to X⁸ is CH or N; Ar¹ has the samegroup defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹—Y²) is abindentate ligand, Y1 and Y² are independently selected from C, N, O, P,and S; L is an ancillary ligand; m is an integer value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹—Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹—Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidationpotential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

M is a metal; (Y³—Y⁴) is a bindentate ligand, Y³ and Y⁴ areindependently selected from C, N, O, P, and S; L is an ancillary ligand;m is an integer value from 1 to the maximum number of ligands that maybe attached to the metal; and m+n is the maximum number of ligands thatmay be attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³—Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, triazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atome,sulfur atom, silicon atom, phosphorus atom, boron atom, chain structuralunit and the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfanyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, host compound contains at least one of the followinggroups in the molecule:

R¹ to R⁷ is independently selected from the group consisting ofhydrogen, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl,heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it hasthe similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule used ashost described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integerfrom 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

R¹ is selected from the group consisting of hydrogen, alkyl, alkoxy,amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl and heteroaryl,when it is aryl or heteroaryl, it has the similar definition as Ar'smentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atomsO, N or N, N; L is an ancillary ligand; m is an integer value from 1 tothe maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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Two emitters are placed into a device EML and caused to emitsimultaneously. λ1 is the maximum wavelength of emitter 1 when notcombined with another emitter. λ2 is the maximum wavelength of emitter 2when not combined with another emitter. λ1>λ2. Then, λ3, the maximumwavelength of the resulting emission (λ1>λ3>λ2) can be tuned by relativeconcentrations of the emitters 1 and 2. Devices were fabricated andspectra measured for a variety of different combinations of emitters. EL(electroluminescent) properties for the various emitters used in theexperiments are shown in Table 2

TABLE 2 EL properties of the emitters used in the device examples 1931CIE λ max FWHM Emitter x Y [nm] [nm] A 0.321 0.626 524 64 B 0.428 0.554552 84 C 0.647 0.350 618 72 D 0.688 0.308 630 52

Example 1

FIG. 3 shows a schematic structure of devices that were fabricatedhaving variable [%] of emitters C and D, used with Example 1.

Example 1 is based on devices having 2 emitters, C and D, deposited intothe device EML in a variety of ratios, but with total concentration ofthe emitters constant C[%]+D [%]=7%. The devices EL is shown (FIG. 4)and the devices performance is summarized in Table 3:

TABLE 3 EL, JVL, LT performance of the devices Example 1 with variable[%] of emitters C and D At Example 1 At 1,000 nits At 40 mA/cm² CD 1931CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) C % D % x y[nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 7 0.690 0.307630 50 8.7 13 18.8 4.7 2 4,145 8 1 6 0.689 0.309 630 52 8.7 14 19.8 5.12 4,482 10 3 4 0.684 0.313 628 52 8 15.2 20.4 5.9 4 4,920 16 4 3 0.6800.318 628 52 8.1 163 20.4 6.3 12 5,182 38 6 1 0.668 0.329 626 58 7.918.1 19.7 7.2 19 5,834 50 6.25 0.75 0.662 0.335 624 62 7.4 19 18.8 8.111 6,092 28 6.5 0.5 0.659 0.338 622 64 7.3 19.8 18.9 8.6 30 6,503 666.75 0.25 0.654 0.343 622 70 7.2 20.3 18.1 8.9 18 6,680 38 7 0 0.6470.350 618 72 7.4 20.9 17 8.9 18 6,898 35 *Calculated assumingacceleration factor 1.8

FIG. 4 shows electroluminescent (EL) spectra of the devices of Example1.

FIG. 5 shows maximum wavelength and full width half maximum (FWHM)values for the devices of Example 1. Both measured experimental data andresults calculated by adding spectra proportional to emitterconcentration are shown.

FIG. 6 shows the FWHM difference (experimental vs. calculated) valuesfor the devices of Example 1.

Example 1 (and the other examples) show the following:

The resulting experimental EL spectra of the devices measured in theexamples is significantly narrower as compared to theoreticallycalculated superimposed EL spectra of individual emitters C and D (forExample 1, see FIGS. 5 and 6). A similar narrowing is also observed inExamples 3, 4, and 5, but not in Example 2. This narrowing is anunexpected result, which is opposite to results expected as described inmany references (see below), where a broad emission spectra was obtainedby placing 2 emitters in one emissive layer.

-   High-Brightness White Organic Light-Emitting Diodes Featuring a    Single Emission Layer. Chang, Mei-Ying; Wu, Chun-Chih; Lin,    Shih-Chin; Chen, Yi-Fan. Journal of the Electrochemical Society    (2009), 156(1), J1-J5.-   Broad wavelength modulating and design of organic white diode based    on lighting by using exciplex emission from mixed acceptors. Wang,    D.; Li, W. L.; Su, Z. S.; Li, T. L.; Chu, B.; Bi, D. F.; Chen, L.    L.; Su, W. M.; He, H. Applied Physics Letters (2006), 89(23),    23351111-233511/3.-   High-efficiency single dopant white electrophosphorescent    light-emitting diodes. Adamovich, Vadim; Brooks, Jason; Tamayo,    Arnold; Alexander, Alex M.; Djurovich, Peter I.; D'Andrade, Brian    W.; Adachi, Chihaya; Forrest, Stephen R.; Thompson, Mark E. New    Journal of Chemistry (2002), 26(9), 1171-1178.-   White emission from a single-component single-layer solution    processed OLED. Coya, Carmen; Ramos, Maria M.; Luna, Xenia; Alvarez,    Angel Luis; de Andres, Alicia; Blanco, Raul; Juarez, Rafael; Gomez,    Rafael; Segura, Jose Luis Proceedings of SPIE (2009), 7415(Organic    Light Emitting Materials and Devices XIII), 74151P/1-74151P/12.-   Efficient, color-stable fluorescent white organic light-emitting    diodes with single emission layer by vapor deposition from solvent    premixed deposition source. Jou, Jwo-Huei; Chiu, Yung-Sheng; Wang,    Chung-Pei; Wang, Ren-Yang; Hu, Huei-Ching. Applied Physics Letters    (2006), 88(19), 193501/1-193501/3.-   Efficient pure-white organic light-emitting diodes with a    solution-processed, binary-host employing single emission layer.    Jou, Jwo-Huei; Sun, Ming-Chen; Chou, Hung-Hsing; Li, Chien-Hung.    Applied Physics Letters (2006), 88(14), 141101/1-141101/3.-   White light emission from a single layer organic light emitting    diode fabricated by spincoating. Yang, J. P.; Jin, Y. D.;    Heremans, P. L.; Hoefnagels, R.; Dieltiens, P.; Blockhuys, F.;    Geise, H. J.; Van der Auweraer, M.; Borghs, G. Chemical Physics    Letters (2000), 325(1, 2, 3), 251-256.

Table 3 and FIGS. 4 and 5 illustrate that maximum wavelength, FWHM, anddevice CIE can be fine tuned in a predictable way within a range definedby individual emitters C and D by the changing of the relative % ofemitters C and D in the device EML.

Examples 2, 3, 4 and 5 show results similar to those of Example 1, butfor different combinations of emitters.

Example 2

FIG. 7 shows schematic structure for the devices of Example 2 withvariable [%] of emitters A and B.

FIG. 8 shows EL spectra of the devices of Example 2 with variable [%] ofemitters A and B.

FIG. 9 shows maximum wavelength and FWHM values for the devices inExample 2 with variable [%] of emitters A and B. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

Table 4 shows EL, JVL, and LT performance of the devices of Example 2with variable [%] of emitters A and B.

TABLE 4 EL, JVL, LT performance of the devices Example 2, with variable[%] of emitters A and B At Example 2 At 1,000 nits At 40 mA/cm² AB 1931CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) A % B % x y[nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 12 0.4280.554 552 84 5.9 47.6 14.2 25.2 224 14,494 115 3 9 0.421 0.560 550 825.7 50.4 14.9 27.7 275 15,152 130 6 6 0.407 0.571 548 82 5.6 54.6 15.930.7 215 16,208 90 8 4 0.396 0.578 546 82 5.4 55.9 16.2 32.3 152 16,78160 9 3 0.388 0.583 544 82 5.4 58.1 16.7 33.6 145 17,123 55 10 2 0.3750.592 538 82 5.3 57.6 16.4 34.4 174 17,264 65 11 1 0.354 0.606 528 745.3 58.9 16.6 35.1 108 17,400 40 11.5 0.5 0.341 0.614 526 70 5.2 57.516.1 34.8 67 17,038 26 12 0 0.321 0.626 524 64 5.3 57.4 16 33.8 4816,700 19 *Calculated assuming acceleration factor 1.8

Example 3

FIG. 10 shows a schematic structure for the devices in Example 3 withvariable [%] of emitters B and C.

FIG. 11 shows EL spectra for the devices of Example 3 with variable [%]of emitters B and C.

FIG. 12 shows maximum wavelength and FWHM values for the devices ofExample 3 with variable [%] of emitters B and C. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

Table 5 shows EL, JVL, and LT performance of the devices of Example 3with variable [%] of emitters B and C.

TABLE 5 EL, JVL, LT performance of the devices Example 3 with variable[%] of emitters B and C At Example 3 At 1,000 nits At 40 mA/cm² BC 1931CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) B % C % x y[nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 12 0.6550.343 622 74 6.7 16.6 14.9 7.7 15 5,729 40 3 9 0.652 0.346 620 74 6.917.8 15.4 8.0 28 6,323 63 6 6 0.645 0.351 618 72 6.9 19.2 15.5 8.7 376,986 70 8 4 0.640 0.356 618 72 6.8 21.3 16.3 9.9 108 7,766 170 9 30.634 0.362 618 72 6.7 22.8 16.6 10.6 165 8,303 230 10 2 0.616 0.379 60870 6.7 26.4 16.9 12.4 193 9,552 210 11 1 0.590 0.404 606 68 6.5 31.217.2 15.1 217 11,082 180 11.5 0.5 0.553 0.439 602 72 6.2 36.8 17.1 18.6174 12,886 110 12 0 0.457 0.530 562 90 5.9 47.3 14.8 25.2 63 15,789 28*Calculated assuming acceleration factor 1.8

Example 4

FIG. 13 shows a schematic structure for the devices of Example 4 withvariable [%] of emitters A and D.

FIG. 14 shows EL spectra for the devices of Example 4 with variable [%]of emitters A and D.

FIG. 15 shows maximum wavelength and FWHM values for the devices ofExample 4 with variable [%] of emitters A and D. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

Table 6 shows EL, JVL, and LT performance of the devices of Example 4with variable [%] of emitters A and D.

TABLE 6 EL, JVL, LT performance of the devices Example 4 with variable[%] of emitters A and D At Example 4 At 1,000 nits At 40 mA/cm² AD 1931CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) A % D % x y[nm] [nm] [V] [Cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 10 0.6880.308 630 52 9.6 10.9 15.3 3.5 1 3372 8 3 9 0.691 0.307 630 54 7.8 11.817.1 4.7 3 3,885 15 6 6 0.687 0.310 630 50 7.7 13.3 18.8 5.4 6 4,503 268 4 0.681 0.315 630 50 7.3 14.6 19.6 6.3 11 5,057 36 9 3 0.674 0.321 62848 7.3 15.9 20.1 6.8 18 5,492 52 10 2 0.657 0.336 626 48 6.9 18.2 20.68.3 19 6,353 42 11 1 0.614 0.375 626 44 6.6 23.1 20.7 11.0 17 7,850 2611.5 0.5 0.548 0.434 622 44 6.1 29.9 19.8 15.4 10 10,020 10 12 0 0.3560.604 528 76 5.4 54.4 15.2 31.8 20 16,738 8 *Calculated assumingacceleration factor 1.8

Example 5

FIG. 16 shows a schematic structure for the devices of Example 5 withvariable [%] of emitters B and D.

FIG. 17 shows EL spectra for the devices of Example 5 with variable [%]of emitters B and D.

FIG. 18 shows maximum wavelength and FWHM values for the devices ofExample 5 with variable [%] of emitters B and D. Both measuredexperimental data and results calculated by adding spectra proportionalto emitter concentration are shown.

FIG. 19 shows chemical structures for compounds used in devicefabrication

Table 7 shows EL, JVL, and LT performance of the devices of Example 5with variable [%] of emitters B and D.

TABLE 7 EL, JVL, LT performance of the devices Example 5 with variable[%] of emitters B and D At Example 5 At 1,000 nits At 40 mA/cm² BD 1931CIE λ_(max) FWHM Voltage LE EQE PE 10,000 nits L₀ LT_(97%) B % D % x y[nm] [nm] [V] [cd/A] [%] [lm/W] LT_(97%) [h]* [nits] [h] 0 10 0.6880.308 630 52 9.6 10.9 15.3 3.5 1 3372 8 4 8 0.69 0.31 632 52 7.6 12.618.3 5.2 6 4,172 29 6 6 0.687 0.31 630 50 7.6 14 19.8 5.7 9 4,770 36 8 40.677 0.32 628 50 7.5 14.9 19.2 6.2 32 5,265 100 10 2 0.646 0.35 626 467.1 19.5 20 8.6 46 6,888 90 11 1 0.6 0.39 624 46 6.8 24.7 19 11.3 798,524 105 11.5 0.5 0.541 0.45 622 48 6.4 32.1 17.5 15.8 64 10,888 55 120 0.457 0.53 562 90 5.9 47.3 14.8 25.2 63 15,789 28 *Calculated assumingacceleration factor 1.8

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A first device, comprising: an anode; acathode; an emissive layer disposed between the anode and the cathode,the emissive layer further comprising: a first organic emitting materialhaving a first peak wavelength; a second organic emitting materialhaving a second peak wavelength; wherein the emissive layer has ahomogenous composition; wherein the second peak wavelength is between 0and 40 nm greater than the first peak wavelength.
 2. The first device ofclaim 1, wherein the first and second organic emitting materials arephosphorescent organic light emitting materials.
 3. The first device ofclaim 1, wherein the second peak wavelength is between 12 and 28 nmgreater than the first peak wavelength.
 4. The first device of claim 1,wherein the FWHM of the emissive spectrum of the first device is lessthan the greater of the FWHM of the emissive spectrum of: (i) a seconddevice that is the same as the first device in all respects except thatit includes the first emitting material but not the second emittingmaterial, and (ii) a third device that is the same as the first devicein all respects except that it includes the second emitting material butnot the first emitting material.
 5. The first device of claim 1, whereinthe first device emits a third peak wavelength that is between the firstpeak wavelength and the second peak wavelength.
 6. The first device ofclaim 1, wherein: the first device emits a third peak wavelength that isbetween the first peak wavelength and the second peak wavelength; theconcentration of the first organic emitting material in the emissivelayer is C1, the concentration of the second organic emitting materialin the emissive layer is C2, the first, second and third peakwavelengths are λ1, λ2, and λ3, respectively, and the third peakwavelength λ3 is within 4% of:((λ1 C1)+(λ2 C2))/(C1+C2).
 7. The first device of claim 1, wherein themeasured FWHM of the emissive spectrum of the first device is less thanthe combined emission of the first and second emitting materialscalculated based on the proportions of the first and second emittingmaterials present in the emissive layer.
 8. The first device of claim 1,wherein the measured FWHM of the emissive spectrum of the first deviceis at least 10% less than the combined emission of the first and secondemitting materials calculated based on the proportions of the first andsecond emitting materials present in the emissive layer.
 9. The firstdevice of claim 1, wherein the first device is an organic light emittingdevice.
 10. The first device of claim 1, wherein the first device is apanel comprising a plurality of organic light emitting devicescontrolled by an active matrix.
 11. The first device of claim 1, whereinthe first device is a consumer product.